questions about "find_if_case"

[Eric Fisher]

Hi,

  For if-conversion pass (pass_if_after_combine), we can see there're
some IF-THEN-ELSE cases which we try to transform. Let's say
find_if_case_1, for an example.

     (1)
        if (test) goto over; // x not live
        x = a;
        goto label;
        over:

   becomes

        x = a;
        if (! test) goto label;

   One of my questions is what the benefit this convertion can attain?

   Also, there's a precondition, which the THEN bb must cost cheap
then BRANCH_COST. I'm not clear about the reason.

   Thanks in advance.

   Best wishes,
   Eric